Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
249 PM EDT Sat Jul 03 2021
Valid 12Z Tue Jul 06 2021 - 12Z Sat Jul 10 2021
...Elsa is forecast to impact Florida and the Southeast through
the middle of next week with heavy rainfall and potential for high
winds...
...Repeating heavy rain is likely to persist over southern Texas
through much of next week as low pressure lingers...
...Overview...
In a fairly typical summer pattern, expect a strengthening upper
ridge to prevail over the Great Basin/Desert Southwest while
varying degrees of mean troughing align over the east-central U.S.
A leading shortwave crossing the northeast quadrant of the lower
48 will push along a wavy cold front during most of next week. A
trailing Pacific shortwave rounding the upper ridge should amplify
into the Midwest/western Great Lakes toward the end of the week,
supporting another area of low pressure and associated frontal
system. The primary features of interest at lower latitudes will
be Tropical Storm Elsa which should impact Florida and parts of
the Southeast through the middle of next week, and a slow-moving
upper trough/low that could produce heavy rainfall as it slowly
drifts over Texas and into northern Mexico.
...Guidance/Predictability Evaluation...
Overall a 00Z/06Z model blend transitioning to a model/ensemble
mean blend provided a good starting point to reflect the most
common themes of guidance while downplaying details that have
lower confidence/predictability. For Elsa, the 06Z GFS provided
the best template relative to latest National Hurricane Center
advisories valid Tuesday-Thursday. ECMWF/UKMET runs are somewhat
slower while the CMC is holding onto its recent typical fast bias.
Over the past day or so the ECMWF has trended considerably toward
the GFS for track while the GFS has trended weaker. Meanwhile
there is good agreement in principle for the shortwave crossing
the northeastern quadrant of the lower 48 and a second shortwave
amplifying into the Midwest after rounding the western upper
ridge. In both cases but especially for the latter, there are
detail differences that have a meaningful effect on the surface
evolution--but low predictability 5-7 days out in time. The blend
approach reflects the most agreeable aspects of synoptic evolution
while awaiting better clustering for specifics.
...Weather Highlights/Hazards...
An upper low/trough drifting southwest over southern Texas into
northern Mexico through next week will support a repeating heavy
rain threat over that region most days, with multi-inch totals
expected and localized five-day totals over a foot likely (though
the heaviest looks to be just south of the Rio Grande). Farther
northwest, late-day monsoonal type showers and thunderstorms are
likely to continue through Wednesday over the Central/Southern
Rockies. Any activity thereafter should be much lighter and more
scattered. Around midweek Elsa will bring the potential for heavy
rainfall, flooding, and high winds to parts of Florida and areas
northeastward over the Southeast and southern Mid-Atlantic. Though
somewhat less dramatic than in previous days, considerable spread
still exists for Elsa's strength/track/timing along with
associated effects. Monitor products from the National Hurricane
Center for the latest information regarding Elsa. The wavy front
pushing east from the Midwest/Great Lakes will produce periods of
rain that could be locally moderate/heavy. After midweek the
tropical moisture from Elsa could increase rain totals in the
Mid-Atlantic/Northeast depending on Elsa's track/strength and any
frontal interaction. The system forecast to reach the
Midwest/Great Lakes toward the end of the week may be accompanied
by meaningful rainfall as well.
Expect the heat wave over a significant portion of the West to
continue through next week as the Great Basin/Southwest upper
ridge restrengthens. The Northwest and northern Great Basin should
see highs 10-15F above normal most days with locally higher
readings possible early and late in the period. For a brief time
around Wednesday-Thursday some locations may be a little less
above normal as a Pacific shortwave rounding the upper ridge
brings a weak cold front through. Some daily records for
highs/warm lows will be possible ahead of this weak front, while
such potential could also be worth monitoring as the upper ridge
rebounds late in the week. The southern High Plains/Texas will
likely see highs 5-12F below average for most of the week due to
cloudiness and rain from the persistent upper level disturbance
there.
Rausch/Jackson
Additional 3-7 Day Hazard information can be found on the WPC
medium range hazards outlook chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php
WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation, winter weather outlook probabilities
and heat indices are at:
https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif
https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif
https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html
https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml
https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml